We do not mean what has your friend borrowed and has not given back yet.
We are referring to the lead up to Easter in the Christian Calender which is name for the time of reflection and fasting on the way to Easter which remembers Jesus’s forty days in the Desert. More about Jesus’s time in the Desert can be found in the Gospels of Luke, Matthew and Mark, but not John . Ash Wednesday is actually a few days more than forty days before Easter as in previous times people were allowed not to fast on Sundays so Sundays were not counted as days. This is why we have Shrove Tuesday also known as Pancake Day, as in previous times food such as eggs were used up on this day, so they did not go to waste in the time of fasting ahead. In 2021 Shrove Tuesday is on the 16th of February, so Ash Wednesday is on 17th February.
Updated (Feb 22) In 2022 Shrove Tuesday is on the 1st of March and so Ash Wednesday is the 2nd of March.
The name for Lent in the original liturgical calender is Quadragesima in Latin. the Quad part of the name is 40 for the 40 days (incidentally the word Quarantine is also from a similar origin as ships with pestilence on board were quarantined for 40 days).
Nowadays most people do not fast although some give up luxuries such as Chocolate and others use the time for Charity Fundraising or otherwise doing good works. Some Churches remove all floral displays from there buildings, and cover decorated statues during Lent the greater to observe the magnificence of Easter decorations.